给排水专业英语论文.doc

Title：_ _ _Disinfection _ College _ _ Major _ Water and Wastewater Engineering _Class _ CE 1001 _Number _ _Name _ _Date _ 2012.12.08 _ 5WWE Final Class Project Student Name: Fang JieTechnology Development of DisinfectionAbstract: As an important measure in water purification, chlorination, which had hitherto been routine of water disinfection is being to be doubted due to the disinfection by-products which have potential carcinogenic effects. There are two ways to solve this urgent problem, to improve the chlorination and to create new measures for water disinfection. In this paper the advances in this field home and abroad are presented, especially the chlorine, chlorine dioxide, ozone and ultraviolet processes are compared.Keywords: Disinfection; Chlorine; Chlorine Dioxide; Ozone; Ultraviolet1. Disinfection conceptA potable water must be more than crystal clearit must be completely free of disease causing microorganisms. To accomplish this, the final treatment process in water treatment process in water treatment plants is disinfection, which destroys or inactivates the pathogens. 2. Disinfection historyThe safe drinking water affects health, social stability and economic development. It has been one of the serious challenges faced by China and the world. Cut off the way through drinking water spread disease, drinking water treatment disinfection as the final process is essential. It has a lot of water disinfection methods, mainly chlorine disinfection, ozone disinfection, chlorine dioxide disinfection, ultraviolet disinfection.2.1 Chlorine disinfection: The beginning of chlorine is water deodorant instead disinfectant. It is recorded that about 1835 a proposal to make it palatable in swamp water chlorination. English used a bleach solution to disinfect the water pipe network after typhoid epidemic in 1897. Chlorine as a conventional water treatment processes, and is generally believed to begin from 1902, by Maurice Duyk in Belgian using chlorinated lime and iron per-chlorate before the filter for Middlelkerke city water supply. Pre-chlorination process was introduced to the United States as coagulation aid measures in 1914 and disinfection breakpoint chlorination experiments were conducted in 1940. 2.2 Ozone disinfection: The first ozone treatment of drinking water is from the end of the 19th century in Germany, the Netherlands and France. Before the Liberation, the Chinese had used a German ozone generator for a small amount of drinking water treatment, began to study the ozone generator in 1964, and began to be used in practice in 1969.2.3 Chlorine dioxide disinfection: In 1900, some people try to use chlorine dioxide disinfection. In 1944, the large-scale applications in the Niagara Falls Water Treatment Plant controlled the taste and odor of phenol. 1950s, chlorine dioxide gradually been applied in the field of drinking water disinfection. 1970s, chlorine dioxide is widely accepted as a drinking water disinfectant, and hundreds of waterworks in Europe and the United States have begun to use chlorine dioxide as a disinfectant. In recent years, China began the trial of chlorine dioxide or chlorine dioxide - chlorine hybrid disinfection, to obtain a significant effect.2.4 UV disinfection: 1909-1910, UV disinfection equipments experimental application in Marseille waterworks in France is successful, the scale for the 25m/ h. So far, using UV disinfection of drinking water treatment plants in Europe is over 2000. It was found that the UV light has a significant effect in the control of the protozoon, so UV disinfection gradually becomes an important means of water treatment.3. Disinfection process and using5 principal mechanisms proposed to explain action of disinfectants: (1) Damage to the cell wall (result in cell lyses and death). (2) Alteration of cell permeability. (3) Alteration of the colloidal nature of the protoplasm (e.g. heat, radiation). (4) Alteration of the organisms DNA or RNA (e.g. UV irradiation). (5) Inhibition of enzyme activity (oxidizing agents e.g. chlorine).3.1 Chlorine disinfection:Chlorine is a yellow-green gas under standard conditions, where it forms diatomic molecules. It has the highest electron affinity and the third highest electro negativity of all the elements; for this reason, chlorine is a strong oxidizing agent. Chlorination disinfection as a traditional drinking water method has been in use ever since. When Cl2 is added to water, it rapid hydrolysis to HOCl. Cl2+H2O HOCl+ H+ Cl (1)HOCl is a weak acid and will dissociate. HOCl H + OCl (2)It is depends on pH: (1) At pH 1.0, HOCl reverts back to Cl(depends on chloride concentration). (2) At pH 4.0-6.0, HOCl is favored (because a weak acid and dissociates poorly when pH 7.5 and at 0oC and pH 7.8, favor OCl. (4) PH 9.0 and above, favor OCl.Chlorine existing in the form HOCl and/or OCl is defined free (available) chlorine. HOCl is more germicidal (effective disinfectant) than OCl. Discovered in recent years, in the chlorination, many organics contaminated water through chlorination, can produce THMs and other halogenated byproducts, these byproducts, and chloroform is considered important carcinogens.The chlorine disinfection has many advantages: (1) Chlorine Germicidal ability. (2) In the water, it can keep a certain amount of residual chlorine long time, and has continued disinfection. (3) The use is more convenient and lower cost.The chlorine disinfection shortcomings: (1) Product harmful disinfection by-products. (2) The ability to virus inactivation than chlorine dioxide, ozone, etc. (3) Unsafe.3.2 Ozone disinfection: Advantages: (1) Ozone has a Very high oxidation potential (very strong oxidizing agent). (2) Easily decomposes producing oxygen and free hydroxyl radicals-at 20C, the half life is 72 hrs. (3) Much stronger than chlorine (disinfects E.coli 2800x faster than chlorine). (4) Even stronger oxidant when dissolved in water. (5) Do not form THMs. Disadvantages: (1) Expensive. (2) Short circuiting can occur due to short contact time reactors. (3) No disinfecting residual. (4) Product harmful by-products.3.3 Chlorine dioxide disinfection:Chlorine dioxide disinfection has the following advantages: (1) Bactericidal effect with less, the role of fast and long duration of disinfection, and can maintain a residual disinfectant amount. (2) Oxidizing is better, can break down the cell structure, and can kill spores. (3) Can control iron, manganese. (4) Affect small by temperature and pH. (5) Do not produce trihalomethanes and haloacetic acids.The main disadvantages of the chlorine dioxide disinfection: (1) Chlorine dioxide disinfection generates the inorganic disinfection by-products. (2) Chlorine dioxide itself is harmful, especially in the high concentration. (3) The preparation, use of ch